Egr device for internal combustion engine

ABSTRACT

Provided is an EGR device that allows an EGR valve to be removed with ease even when the EGR valve is provided adjacent to a turbocharger. The EGR device includes a first connecting pipe portion ( 41   b ) extending from a compressor of the turbocharger and having a first annular shoulder surface ( 41   c ) at a base end thereof, an EGR valve ( 65 ) fixedly attached to a part of the engine, a joint member ( 71 ) including a flange ( 71   a ) attached to the EGR valve ( 65 ) and a second connecting pipe portion ( 71   b ), and opposing the first connecting pipe portion in a coaxial relationship, the second connecting pipe portion being provided with a second annular shoulder surface ( 71   c ) at a base end thereof, and a flexible pipe member ( 72 ) having a first end fitted onto the first connecting pipe portion and a second end fitted onto the second connecting pipe portion. A distance (L 2 ) between the two annular shoulder surfaces is greater than a length (L 1 ) of the flexible pipe member by a prescribed distance.

TECHNICAL FIELD

The present invention relates to an EGR (exhaust gas recirculation) device for an internal combustion engine equipped with a supercharger such as a turbocharger.

BACKGROUND ART

In a known EGR device for an internal combustion engine, an EGR valve is attached to a cylinder row end of a cylinder head, and internally defines a part of an exhaust gas passage that extends from an exhaust system. The upstream end of the exhaust gas passage is connected to a converging part of an exhaust manifold via an exhaust gas introduction pipe, and the downstream end of the exhaust gas passage is connected to an intake passage of an intake manifold via an exhaust gas injection pipe. See JP2000-87807A, for instance.

An engine is often equipped with a supercharger such as a turbocharger for the purpose of improving fuel economy. A turbocharger supplies compressed air into the combustion chambers of the engine so that the volumetric efficiency is improved and a high engine input can be obtained for the given engine displacement of the engine. In an engine equipped with a turbocharger, both a high-pressure EGR device that recirculates the high-pressure exhaust gas in an upstream part of the exhaust system to the intake air under high pressure, and a low-pressure EGR device that recirculates the low-pressure exhaust gas in a downstream part of the exhaust system to the intake air under negative pressure are employed at the same time. As a result, the structure of the intake system and the exhaust system tends to be highly complex owing to the presence of these EGR devices. To allow a compact design of the intake system and the exhaust system, it is a common practice to place at least one of the EGR valves adjacent to the turbocharger.

When an EGR valve is positioned adjacent to a turbocharger, because the associated piping and other components bunch up around the turbocharger, it becomes difficult to remove the EGR valve for maintenance purpose. Oftentimes, it is necessary to remove the turbocharger itself to remove or replace the EGR valve.

The present invention was made in view of such problems of the prior art, and has a primary object to provide an EGR device that allows an EGR valve to be removed with ease even when the EGR valve is provided adjacent to a supercharger.

To achieve such an object, the present invention provides a An EGR device for a multiple-cylinder engine equipped with a supercharger (41) for returning a part of exhaust gas expelled from an exhaust system of the engine to an intake system of the engine, comprising: a first connecting pipe portion (41 b) extending from a compressor of the supercharger and having a first annular shoulder surface (41 c) at a base end thereof; an EGR valve (65) fixedly attached to a part of the engine; a joint member (71) including a flange (71 a) attached to the EGR valve (65) and a second connecting pipe portion (71 b) defining a passage communicating with an inlet end of the EGR valve, and opposing the first connecting pipe portion in a coaxial relationship, the second connecting pipe portion being provided with a second annular shoulder surface (71 c) at a base end thereof; and a flexible pipe member (72) having a first end fitted onto the first connecting pipe portion and a second end fitted onto the second connecting pipe portion; wherein a distance (L2) between the two annular shoulder surfaces is greater than a length (L1) of the flexible pipe member by a prescribed distance.

According to this arrangement, by moving the joint member (optionally along with the flexible pipe member) in the axial direction away from the EGR valve, the EGR valve can be removed without requiring any major components such as the supercharger to be removed. The axial movement of the joint member is permitted until the two ends of the flexible pipe member abut the respective annular shoulder surfaces.

In a preferred embodiment of the present invention, the supercharger consists of a turbocharger including a turbine for powering the compressor and attached to a part of the engine such that the compressor projects from an exhaust side part of the engine beyond a cylinder row end part of the engine, and the first connecting pipe portion (41 b), the EGR valve (65), the flexible pipe member (72) and the second connecting pipe portion (71 b) extend from the compressor along the cylinder row end part of the engine.

Thereby, the EGR device can be installed in an area adjoining the main body of the engine in a highly compact manner.

The EGR device may further comprises an upstream EGR pipe assembly (62-64) communicating a part of the exhaust system to the inlet end of the EGR valve, the upstream EGR pipe assembly (62-64) including a part generally extending vertically along the cylinder row end part of the engine toward a downstream part of the exhaust system of the engine.

This also contributes to the compact arrangement of the EGR device.

Preferably, an exhaust gas purification device is positioned on an exhaust side of the engine under the turbine, and an upstream end of the upstream EGR pipe assembly is connected to a downstream part of the exhaust gas purification device.

Thereby, the low-pressure exhaust gas having a relatively low temperature is returned to the intake system of the engine, and is mixed with the intake air under negative pressure. The exhaust gas contains moisture of a certain acidity, but the acidity of the exhaust gas is reduced by the catalytic converter before being returned to the intake system. Therefore, the thermal degradation of the flexible pipe member can be minimized.

According to a preferred embodiment of the present invention, the upstream EGR pipe assembly extends generally upward from the upstream end thereof between the engine and the exhaust gas purification device, and along the cylinder row end part of the engine toward the intake side of the engine before doubling back toward the exhaust side of the engine and being connected to the inlet end of the EGR valve.

This also contributes to the compact arrangement of the EGR device.

The upstream EGR pipe assembly may comprise an EGR cooler (63).

Thereby, the temperature of the exhaust gas conducted to the flexible pipe member can be lowered by the EGR cooler so that the thermal degradation of the flexible pipe member can be minimized.

The upstream EGR pipe assembly may include a rigid pipe member (64) connected between the EGR cooler and the EGR valve.

The rigid pipe member may be fixedly attached to a suitable part of the engine so that the EGR valve (on the downstream end of the rigid pipe member) and the EGR cooler (on the upstream end of the rigid pipe member) can be fixedly secured to the engine in a highly stable manner without requiring additional brackets.

In a particularly preferred embodiment of the present invention, a plurality of threaded bolts (81, 82) are passed through a flange (64 b) provided on a downstream end of the rigid pipe member of the upstream EGR pipe assembly, the EGR valve (65) and the joint member (71) to fasten these components to one another.

Thereby, the EGR valve and the joint member can be fixedly secured to the rigid pipe member of the upstream EGR pipe assembly in a both simple and stable manner.

Preferably, the threaded bolts include at least a pair of stud bolts each having a base end threaded into one of the flange (64 b) of the rigid pipe member and the flange (71 a) of the joint member, and a free end having a threaded portion having a nut (83) fastened thereon.

Thereby, the rigid pipe member, the EGR valve and the joint member can be assembled together in a proper alignment with one another with the aid of the stud bolts so that the assembly work can be facilitated. Typically, a gasket is required to be placed between each interface, but this arrangement allows the assembly process to be carried out in a highly efficient manner.

Typically, the free end of each stud bolt is provided with a tool engagement feature (81 a). Thereby, each stud bolt can be installed and removed with ease by engaging a suitable tool with the tool engagement feature.

Alternatively or additionally, the threaded portion on the free end of each stud bolt may be provided with a length at least twice as long as a thickness of the nut. Thereby, by threading an additional nut (84) until the additional nut abuts the original nut (a double nut arrangement), the stud bolt can be unscrewed from the flange of the rigid pipe member or the flange of the joint member (as the case may be) by engaging the original nut with a suitable tool.

In a preferred embodiment of the present invention, a first gasket (68) is interposed between the flange of the rigid pipe member of the upstream EGR pipe assembly and the EGR valve, and a second gasket (69) is interposed between the EGR valve and the joint member, and wherein the distance (L2) between the two annular shoulder surfaces is greater than the length of the flexible pipe member (L1) at least by a combined thickness of the two gaskets in an unused state.

According to this arrangement, adequate spaces can be created between the flange of the rigid pipe member of the upstream EGR pipe assembly and the EGR valve, and between the EGR valve and the joint member so that the replacement of the EGR valve can be accomplished without causing any difficulty.

Each end of the flexible pipe member may be secured onto the corresponding connecting pipe portion with a hose band.

Thereby, the flexible pipe member can be installed in a both simple and economical manner.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a plan view of an engine of a motor vehicle equipped with an EGR device embodying the present invention;

FIG. 2 is a block diagram of an intake system and an exhaust system of the engine;

FIG. 3 is a fragmentary perspective view of a low-pressure EGR device shown in FIG. 2;

FIG. 4 is a fragmentary sectional view of a part of the low-pressure EGR device;

FIG. 5 is an exploded perspective view of a part of the low-pressure EGR device; and

FIG. 6 is a view similar to FIG. 4 when the low-pressure EGR device is being disassembled.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

An embodiment of the present invention is described in the following with reference to the appended drawings. An engine 4 consisting of an in-line four-cylinder diesel engine is positioned in an engine room 3 formed in a front part of a vehicle body 2 of a motor vehicle 1.

The engine 4 is laterally mounted in the engine room 3, and slightly offset in the rightward direction. The engine 4 is supported by the vehicle body 2 via an engine mount (not shown in the drawings) with a slight rearward slant. A transmission system is connected to a lower side of a left end part of the engine 4. A pair of front side frames 6 (only one of them is shown in FIG. 1) extend along either side of the engine room 3, and a pair of damper bases 7 are positioned on either side of a rear end part of the engine room 3.

A rectangular battery 8 is positioned on an inboard side of the left damper base 7 with the long side of the battery 8 extending in the fore and aft direction. An ECU unit 9 for controlling various parts of the vehicle 1 is provided immediately ahead of the battery 8, and an air cleaner 10 is positioned immediately ahead of the ECU unit 9. A relay box 11 which is elongate in the fore and aft direction is positioned on the outboard side of the battery 8.

A front bulkhead (not shown in the drawings) supporting a radiator (not shown in the drawings) is provided in a front end part of the engine room 3. A cover member 12 is positioned on top of the front bulkhead. The engine 4 is provided with an intake/exhaust system 18 consisting of an intake system 20 for supplying air to the engine 4 and an exhaust system 30 for expelling exhaust gas from the engine 4. The exhaust system 30 is provided with a turbocharger 40 which is powered by the flow of the exhaust gas and compresses the intake air supplied to the engine 4. A high-pressure EGR device 50 is provided in a downstream part of the turbocharger 40, and a low-pressure EGR device 60 is provided in an upstream part of the turbocharger 40, each for returning a controlled amount of the exhaust gas to the intake system 20.

FIG. 2 is a block diagram illustrating the overall structure of the intake/exhaust system 18. In the intake system 20, air drawn from the atmosphere is introduced into a first intake duct 21 via an intake inlet 21 a, and is then conducted to a throttle valve 23 via an air cleaner 10 and a second intake duct 22. Then, after being compressed by a compressor 41 of the turbocharger 40, the intake air is forwarded to an intercooler 25 via a third intake duct 24, and to an intake manifold 29 via a fourth intake duct 26, an intake shutter valve 27 and a fifth intake duct 28.

In the exhaust system 30, the exhaust gas collected from the engine 4 by an exhaust manifold 31 is forwarded to a turbine 42 of the turbocharger 40, and is expelled to the atmosphere via a first exhaust pipe 32, a catalytic converter 33, a DPF 34, and a second exhaust pipe 35. The high-pressure EGR device 50 includes a first high-pressure EGR pipe 51 directly connected to the exhaust manifold 31, a high-pressure EGR valve 52, and a second high-pressure EGR pipe 53 connected to the downstream side of the intake shutter valve 27, in this order from the side of the exhaust system 30. The low-pressure EGR device 60 includes an EGR filter device 61 connected to the DPF 34, a first low-pressure EGR pipe 62, a low-pressure EGR cooler 63, a second low-pressure EGR pipe 64, a low-pressure EGR valve 65, and a third low-pressure EGR pipe 66 connected to the downstream side of the throttle valve 23, in this order from the side of the exhaust system 30.

The throttle valve 23 controls the intake air amount and the intake pressure of the intake air supplied into the cylinders of the engine 4. The intake shutter valve 27 is configured to selectively reduce the intake air amount by narrowing the intake passage at the valve body to raise the temperature of the exhaust gas when the DPF is required to be regenerated by burning off the particulate matter (PM) collected by the DPF 34, but is otherwise kept fully open.

The first low-pressure EGR pipe 62, the low-pressure EGR cooler 63, and the second low-pressure EGR pipe 64 on the upstream side of the low-pressure EGR valve 65 may be collectively referred to as an upstream EGR pipe assembly. In the illustrated embodiment, the second low-pressure EGR pipe 64 forms a part of the upstream EGR pipe assembly.

Referring to FIG. 1 once again, exhaust ports of the engine 4 are provided on the front side of the engine 4. An exhaust converging pipe 36 is attached to a planar mounting surface defined on the front side of the engine 4, and communicates with the exhaust manifold 31 which, in the illustrated embodiment, is internally defined in the cylinder head of the engine 4. The exhaust manifold may also be provided separately from the engine and attached to the front side of the engine 4. The outlet end of the exhaust converging pipe 36 is positioned on the left end side of the engine 4, and is fitted with the turbine 42 of the turbocharger 40.

The turbine 42 is positioned on the front side of the exhaust converging pipe 36, and is provided with a turbine housing and a turbine wheel rotatably supported by the turbine housing around a rotational center line extending in the lateral direction of the vehicle body. The turbine housing defines a turbine inlet extending circumferentially along a tangential direction of the turbine housing, and a turbine inlet extending in the axial direction from a central part of the turbine housing in the rightward direction. The turbine inlet is connected to the outlet end of the exhaust converging pipe 36, and the turbine outlet is connected to the first exhaust pipe 32 connected to the right side wall of the turbine housing.

The first exhaust pipe 32 curves downward as it extends rightward, and is connected to an upper part of the catalytic converter 33 provided under the turbine 42 in a forwardly spaced apart relationship to the exhaust side (the front side) of the engine 4. The catalytic converter 33 removes HC, CO and NOx from the exhaust gas. The DPF 34 (FIG. 2) for trapping particulates from the exhaust gas is provided under the catalytic converter 33. The second exhaust pipe 35 (FIG. 2) is connected to the lower side of the DPF 34, and extends under the engine 4 in the rearward direction. The second exhaust pipe 35 further extends under the floor to a rear end part of the vehicle.

The air cleaner 10 is connected to the downstream end of the first intake duct 21 (FIG. 2) so that the air drawn into the engine room 3 via a front grill is forwarded to the air cleaner 10 via the intake inlet 21 a. An intake outlet is formed on the right side of the air cleaner 10, and is connected to the upstream end of the second intake duct 22. The downstream end of the second intake duct 22 is connected to the left end of the throttle valve 23 which internally defines a laterally extending intake passage.

The compressor 41 of the turbocharger 40 is positioned between the throttle valve 23 and the turbine 42 so as to be coaxial with the turbine 42 and projects beyond the left end of the engine 4. The compressor 41 includes a compressor housing 41 a (FIG. 4) and a compressor wheel rotatably supported by the compressor housing 41 a around a laterally extending rotational center line. The compressor housing 41 a is provided with a compressor inlet provided centrally on the left side wall of the compressor housing 41 a, and a low-pressure EGR introduction port opens out and projects from a rear side of the peripheral wall of the compressor housing 41 a. The compressor housing 41 a is further provided with a compressor outlet extending tangentially from a lower part of the outer peripheral wall of the compressor housing 41 a. The compressor inlet is connected to the intake passage of the throttle valve 23, and the low-pressure EGR introduction port is connected to the EGR gas passage of the low-pressure EGR device 60. The compressor outlet is connected to the intake passage of the third intake duct 24 connected to the lower wall of the compressor housing 41 a.

The turbocharger 40 is provided with a drive shaft 40 a (FIG. 2) connecting the turbine wheel on the side of the exhaust system 30 to the compressor wheel on the side of the intake system 20. The rotational power of the turbine wheel is transmitted to the compressor wheel via the drive shaft 40 a. Thereby, the turbocharger 40 compresses the intake air supplied from the throttle valve 23 and the exhaust gas supplied from the low-pressure EGR device 60, and forwards the mixture at a pressure higher than the atmospheric pressure to the engine 4.

The third intake duct 24 connected to the lower part of the outer periphery of the compressor 41 is connected to the intercooler 25 (FIG. 2) positioned under the cover member 12. The fourth intake duct 26 (FIG. 2) is passed behind the engine 4 via the intercooler 25, and is connected to the intake manifold 29 (FIG. 2) attached to the rear side of the engine 4.

The first high-pressure EGR pipe 51 of the high-pressure EGR device 50 is connected to the right end of the exhaust converging pipe 36 and receives the exhaust gas from the exhaust converging pipe 36. The high-pressure EGR valve 52 is attached to the front side of the cylinder head, and the rear end of the first high-pressure EGR pipe 51 is attached to the front end of the high-pressure EGR valve 52. In the cylinder head of the engine 4, an upstream side passage portion of the second high-pressure EGR pipe 53 (FIG. 2) communicating with the EGR passage of the high-pressure EGR valve 52 is formed so as to extend in the fore and aft direction. The downstream side passage portion of the second high-pressure EGR pipe 53 connected to the rear surface of the engine 4 is connected to the intake introduction portion of the intake manifold 29 and causes the exhaust gas having passed through the high-pressure EGR valve 52 to return to the intake system 20. The downstream side passage portion of the second high-pressure EGR pipe 53 may be connected to a portion other than the intake manifold 29 as long as it is on the downstream side of the compressor 41 in the intake system 20 and on the upstream side of the intake introduction portion.

As shown in FIG. 3, the first low-pressure EGR pipe 62 that extends vertically includes a first upstream flange 62 a disposed at the lower end thereof and fastened to the lower end of the DPF 34 with threaded bolts, and a first downstream flange 62 b disposed at the upper end thereof. The first low-pressure EGR pipe 62 extends rightward from the first upstream flange 62 a, and then curves upward to extend along the right side of the DPF 34 before extending obliquely upward and rearward. The first upstream flange 62 a generally faces to the left, and the first downstream flange 62 b faces obliquely upward and rearward. The lower portion of the vertical section of the first low-pressure EGR pipe 62 is formed as a flexible pipe or a bellows 62 c. As a result, the first upstream flange 62 a and the first downstream flange 62 b can be displaced relative to each other, and stress concentration in the first low-pressure EGR pipe 62 due to thermal expansion of the exhaust system 30 can be avoided.

The EGR filter device 61 consists of a metallic mesh interposed between the first upstream flange 62 a of the first low-pressure EGR pipe 62 and a connecting flange (not shown in the drawings) of the DPF 34. The EGR filter device 61 captures fragments of the DPF 34 and other metallic pieces that might be introduced into the first low-pressure EGR pipe 62.

The low-pressure EGR cooler 63 is provided with a rectangular cooler main body portion 63 a having a laterally elongated cross section and a smaller fore and aft dimension than a vertical dimension. A right end part of the cooler main body portion 63 a is integrally provided with an upstream side connecting pipe portion 63 b extending obliquely downward and forward, and a left end part of the cooler main body portion 63 a is integrally provided with a downstream side connecting pipe portion 63 c extending to the front. Connecting flanges are integrally formed at the free ends of the upstream side connecting pipe portion 63 b and the downstream side connecting pipe portion 63 c, respectively. The cooler main body portion 63 a is provided with a plurality of mounting pieces 63 d for attachment to the engine 4. The cooler main body portion 63 a is positioned between the engine 4 and the catalytic converter 33 which is spaced from the front side of the engine 4, and is attached to the front side of the engine 4 via the mounting pieces 63 d and associated threaded bolts. The cooler main body portion 63 a is configured to circulate the cooling water therein, and cool the exhaust gas by heat exchange between the cooling water flowing through the cooler main body portion 63 a and the exhaust gas.

The second low-pressure EGR pipe 64 is made of a rigid pipe member, and includes a second upstream flange 64 a positioned at the lower end thereof and fastened to the downstream side connecting pipe portion 63 c of the low-pressure EGR cooler 63 by threaded bolts, and a second downstream flange 64 b positioned at the upper end thereof. The second low-pressure EGR pipe 64 extends from the second upstream flange 64 a forward and then toward the left end side of the engine 4 in an upward and leftward direction along a curved path. The second low-pressure EGR pipe 64 is bent again along the left end side of the engine 4 in the rearward direction (toward the intake side). The second low-pressure EGR pipe 64 is then bent upward and forward (toward the exhaust side) making a U turn. In other words, the downstream part of the second low-pressure EGR pipe 64 extends rearward along the cylinder row end part of the engine toward the intake side of the engine, and then doubles back toward the exhaust side of the engine. The second low-pressure EGR pipe 64 is made of metal, and is therefore highly rigid (as opposed to a flexible tube). A connecting piece 64 d for attachment to the engine 4 is provided at an appropriate position of the second low-pressure EGR pipe 64. The second low-pressure EGR pipe 64 is fixed to the engine 4 via a pipe stay 64 e (which is attached to a left end surface of the engine 4) by fastening the connecting piece 64 d to the pipe stay 64 e with a threaded bolt.

FIG. 4 is a longitudinal sectional view of the third low-pressure EGR pipe 66 and the EGR valve 65 which form an essential part of the low-pressure EGR device 60, and FIG. 5 is an exploded perspective view of the third low-pressure EGR pipe 66 and associated parts. As shown in FIGS. 3 and 4, a compressor connecting pipe portion 41 b extends rearward from the rear surface of the rear wall portion of the compressor housing 41 a of the compressor 41. The base end of the compressor connecting pipe portion 41 b is formed with an annular shoulder surface 41 c facing rearward. The annular shoulder surface 41 c protrudes rearward from the surrounding surface of the rear wall portion of the compressor housing 41 a by a prescribed distance in the illustrated embodiment, but may also be defined by a part of the surface of the rear wall portion itself surrounding the compressor connecting pipe portion 41 b.

The third low-pressure EGR pipe 66 includes a joint member 71 positioned on the downstream side of the low-pressure EGR valve 65, a flexible pipe member 72, and a pair of hose bands 73 provided on either axial end of the flexible pipe member 72. As shown in FIGS. 4 and 5, the joint member 71 includes a joint flange portion 71 a and a joint connecting pipe portion 71 b extending forward toward the free end of the compressor connecting pipe portion 41 b. The joint connecting pipe portion 71 b is provided with an annular shoulder surface 71 c facing forward so as to face the annular shoulder surface 41 c in a coaxial relationship. The annular shoulder surface 71 c protrudes forward from the forwardly facing surface of the joint flange portion 71 a by a certain distance in the illustrated embodiment, but may also be defined by a part of the forwardly facing surface of the joint flange portion 71 a surrounding the joint connecting pipe portion 71 b. The joint flange portion 71 a is provided with three bolt holes 70, one centrally in an upper part and two on either lower side part of the joint flange portion 71 a.

The low-pressure EGR valve 65 includes a valve housing 65 a defining a low-pressure EGR passage extending in the front and aft direction, and a disk-shaped butterfly valve 65 d rotatably supported in the valve housing 65 a for opening and closing the low-pressure EGR passage defined in the valve housing 65 a. The two axial ends of the valve housing 65 a define mutually parallel mating surfaces facing in the fore and aft direction. Three bolt holes 65 b extending in the axial direction are passed through respective thick-walled portions 65 c formed on the outer peripheral parts of the valve housing 65 a at a regular angular interval in such a manner that the three bolt holes 65 b align with the respective bolt holes 70 of the joint flange portion 71 a.

The second downstream flange 64 b of the second low-pressure EGR pipe 64 opposes the compressor connecting pipe portion 41 b in a coaxial relationship from the rear and at a certain distance. The second downstream flange 64 b is provided with three bolt holes 64 c, one centrally in an upper part and two on either lower side part of the second downstream flange 64 b. One of the axial end surfaces (the rear axial end surface) of the valve housing 65 a is joined to the second downstream flange 64 b of the second low-pressure EGR pipe 64 via a first gasket 68, and the other axial end surface (the front axial end surface) of the valve housing 65 a is joined to the joint flange portion 71 a of the joint member 71.

The bolt holes 70 of the joint flange portion 71 a consist of female threaded holes passed through the joint flange portion 71 a. A threaded bolt 82 having a threaded part at one end and a hexagonal head at the other end is passed through one of the bolt holes 64 c (the lower right bolt hole 64 c) of the second downstream flange 64 b and the corresponding bolt hole 65 b formed in the thick-walled portions 65 c of the valve housing 65 a, and threaded into the corresponding bolt hole 70 of the joint flange portion 71 a. A stud bolt 81 (threaded bolt) having a threaded part at each end is passed through each of the remaining two bolt holes 64 c (the upper bolt hole 64 c and the lower left bolt hole 64 c) of the second downstream flange 64 b and the corresponding bolt hole 65 b formed in the thick-walled portion 65 c of the valve housing 65 a, and threaded into the corresponding bolt hole 70 of the joint flange portion 71 a. A nut 83 is threaded onto the threaded portion of each stud bolt 82 projecting rearward from second downstream flange 64 b.

As a result, the second downstream flange 64 b of the second low-pressure EGR pipe 64, the low-pressure EGR valve 65 and the joint flange portion 71 a of the joint member 71 are fastened together with the first gasket 68 and the second gasket 69 placed in the interfaces between these three parts. Thus, the fasteners consisting of the threaded bolt 82, the stud bolts 81 and the nuts 83 detachably join the second low-pressure EGR pipe 64, the low-pressure EGR valve 65 and the joint member 71 to one another.

When the second downstream flange 64 b and the low-pressure EGR valve 65 are jointly fastened to the joint flange portion 71 a, the length of the threaded part of each stud bolt 81 protruding from the outer (rear) surface of the second downstream flange 64 b is at least twice the thickness of the nut 83 so that an additional nut 84 (indicated by imaginary lines), in addition to the nut 83, can be threaded onto the protruding part of the stud bolt 81. A tool engaging feature 81 a for engaging a tool is formed at the free end of the stud bolt 81. In the illustrated embodiment, the tool engaging feature 81 a is formed as a projection having a hexagonal cross section. Alternatively, the tool engaging feature 81 a may consist of a projection having any other non-circular cross section, or a non-circular recess as long as it can be used for turning the stud bolt 81 around the central axial line thereof.

The flexible pipe member 72 is made of an elastic material such as synthetic rubber, natural rubber and elastomer (such as urethane rubber and silicone rubber), and is elastically deformable in the lateral direction and the axial direction. The flexible pipe member 72 is disposed between the joint member 71 and the compressor 41, and has an upstream side end portion 72 a fitted over the joint connecting pipe portion 71 b and a downstream side end portion 72 b fitted over the compressor connecting pipe portion 41 b. A pair of annular protrusions 72 c are formed on the outer peripheral surfaces of the upstream side end portion 72 a and the downstream side end portion 72 b of the flexible pipe member 72, respectively, for preventing the axial misalignment of the hose bands 73. Each pair of annular protrusions 72 c are spaced apart from each other by a distance slightly greater than the width of the hose band 73.

Each hose band 73 may consist of a per se known hose band, and the circumferential length thereof can be adjusted, for example, by using a fastening arrangement (not shown) such as a screw. The hose bands 73 clamp the upstream side end portion 72 a and the downstream side end portion 72 b of the flexible pipe member 72 onto the compressor connecting pipe portion 41 b and the joint connecting pipe portion 71 b, respectively, to achieve an air tight connection at these two parts.

When exhaust gas flows through the low-pressure EGR device 60, the second low-pressure EGR pipe 64 and the low-pressure EGR valve 65 are heated, and thermally expand. The flexible pipe member 72 absorbs expansion and contraction of these members, and prevents stress concentration owing to the thermal expansion.

In particular, the length L1 of the flexible pipe member 72 is shorter than the distance L2 between the annular shoulder surface 41 c on the side of the compressor 41 and the annular shoulder surface 71 c on the side of the joint member 71 opposing each other in a state where the low-pressure EGR device 60 is not at a high temperature (a state where maintenance work can be performed). As a result, the axial end surfaces of the flexible pipe member 72 are spaced from the corresponding annular shoulder surfaces 41 c and 71 c by a combined spacing G. In the illustrated example, the corresponding end of the flexible pipe member 72 abuts the annular shoulder surface 71 c so that a space L3 (=L2−L1) is created between the annular shoulder surface 41 c and the front end surface of the flexible pipe member 72.

The dimension L3 of the gap G is selected such that the first gasket 68 and the second gasket 69 both in an unused state (yet to be compressed) can be inserted between the low-pressure EGR valve 65 and the second low-pressure EGR pipe 64, and between the low-pressure EGR valve 65 and the joint member 71, respectively. More specifically, if the thickness of the first gasket 68 is t1 and the thickness of the second gasket 68 is t2, the dimension L3 is greater than the sum of these thicknesses by a certain margin a corresponding to the combined amount of compression of the two gaskets 68 and 69 (L3>t1+t2+α). The thickness of the gasket in an unused state accounts for the thickness of the beads and the warping of the gasket. Therefore, when the stud bolts 81 and the threaded bolt 82 are unfastened, and the hose bands 73 for the flexible pipe member 72 are loosened, it is possible to insert the two gaskets 68 and 69 between the low-pressure EGR valve 65 and the second low-pressure EGR pipe 64, and between the low-pressure EGR valve 65 and the joint member 71, respectively.

The assembling process for the low-pressure EGR device 60 is described in the following.

As shown in FIG. 3, when installing the low-pressure EGR device 60, the low-pressure EGR cooler 63 to which the first low-pressure EGR pipe 62 is connected is attached to the engine 4 via the mounting pieces 63 d. Next, the second upstream flange 64 a of the second low-pressure EGR pipe 64 is connected to the downstream side connecting pipe portion 63 c of the low-pressure EGR cooler 63, and the second low-pressure EGR pipe 64 is attached to the engine 4 via the connecting piece 64 d. Since the second low-pressure EGR pipe 64 is fixed to the engine 4, the supporting rigidity thereof is high and the two stud bolts 81 are also held in a stable condition. As shown in FIG. 5, the two stud bolts 81 are fastened to the joint member 71 in advance so that the two stud bolts 81 extend rearward from the joint flange portion 71 a of the joint member 71.

Thereafter, the two stud bolts 81 are passed into the through holes of the second gasket 69 to temporarily assemble the first gaskets 68 to the joint member 71. Subsequently, the two stud bolts 81 are passed into the bolt holes 65 b of the low-pressure EGR valve 65 to temporarily assemble the low-pressure EGR valve 65 to the joint member 71. Since the two stud bolts 81 are provided in the upper portion and the lower left portion of the second upstream flange 64 a, the position of the low-pressure EGR valve 65 in the directions perpendicular to the axial line of the joint member 71 is correctly determined.

Thereafter, the two stud bolts 81 are passed into the through holes of the first gasket 68 to temporarily assemble the second gasket 69 to the joint member 71. As a result, the first gasket 68, the low-pressure EGR valve 65, the second gasket 69, and the joint member 71 are in a temporarily assembled state so that the relative position in the direction perpendicular to the axial line is correctly determined in a stable manner. Subsequently, while holding this assembly together, the two stud bolts 81 are passed into the bolt holes 64 c of the second low-pressure EGR pipe 64, and the two nuts 83 are threaded onto the stud bolts 81 so that the assembly is pressed onto the second downstream flange 64 b. The nuts 83 are only loosely tightened at this time. In this state, the low-pressure EGR valve 65 and the joint member 71 are suspended by the second low-pressure EGR pipe 64 via the stud bolts 81 in a stable condition. Thereafter, the threaded bolt 82 having the hexagonal head is passed through the bolt holes of these members from behind, and threaded into the bolt hole 70 of the joint member 71. The two nuts 83 and the bolt 82 with a hexagonal head are tightened one after the other so that the second low-pressure EGR pipe 64, the low-pressure EGR valve 65 and the joint member 71 are finally assembled together.

Thereafter, as shown in FIGS. 3 and 4, the upstream side end portion 72 a of the flexible pipe member 72 having the hose band 73 loosely thereof is fitted onto the joint connecting pipe portion 71 b, and the corresponding axial end of the flexible pipe member 72 is brought into contact with the annular shoulder surface 71 c. The hose band 73 is tightened at this position so that the flexible pipe member 72 is connected to the joint connecting pipe portion 71 b in an air tight manner.

Thereafter, to assemble the turbocharger 40 to the engine 4, the compressor connecting pipe portion 41 b is inserted into the downstream side end portion 72 b of the flexible pipe member 72, and the turbocharger 40 is fixedly attached to the engine 4 at appropriate positions. As a result, a gap G having a dimension L3 is created between the annular shoulder surface 41 c and the front end surface of the joint member 71. Finally, the hose band 73 on the downstream side is tightened to connect the downstream side end portion 72 b of the flexible pipe member 72 to the compressor connecting pipe portion 41 b in an air tight manner. This concludes the assembly of the low-pressure EGR device 60 to the engine 4.

Thereafter, the catalytic converter 33 and the DPF 34 are connected to the downstream side of the turbine 42. This can be accomplished without being obstructed by the low-pressure EGR device 60. Further, the first upstream flange 62 a of the first low-pressure EGR pipe 62 is connected to the lower end of the DPF 34. Since the lower portion of the first low-pressure EGR pipe 62 is configured as a bellows 62 c, stress concentration in the first low-pressure EGR pipe 62 due to thermal expansion of the exhaust system 30 can be avoided.

The disassembling process for the low-pressure EGR device 60 for maintenance and other purposes is described in the following.

First of all, as shown in FIGS. 4 and 5, the hose band 73 on the downstream side is loosened, and the two nuts 83 and the bolt 82 are loosened. As a result, the joint member 71 and the flexible pipe member 72 can be moved toward the side of the compressor 41 so that the gap G is created. Subsequently, the bolt 82 is pulled out rearward. The stud bolts 81 are loosened each by engaging the tool engaging feature 81 a with a suitable tool, and are pulled out rearward. If any of the stud bolts 81 is firmly lodged in the threaded hole of the joint flange portion 71 a and cannot be turned, the additional nut 84 may be threaded onto the stud bolt 81 in addition to the original nut 83 so that the two nuts 83 and 84 become locked onto the stud bolt 81. Then, the original nut 83 may be engaged by a spanner or any suitable tool, and is turned in the counter-clockwise direction. Since the effective diameter of the nut 83 is larger than that of the tool engaging feature 81 a, a larger torque can be applied to the stud bolt 81.

Once the stud bolts 81 and the bolt 82 are removed, the low-pressure EGR valve 65 can be removed by sliding the low-pressure EGR valve 65 upward or leftward. If a high frictional resistance is encountered when sliding the low-pressure EGR valve 65 upward or leftward, the joint member 71 and the flexible pipe member 72 may be moved until the flexible pipe member 72 abuts against the annular shoulder surface 41 c. As a result, the distance between the second downstream flange 64 b and the joint member 71 is increased so that the low-pressure EGR valve 65 can be relatively easily slid off. Therefore, the subsequent work of reinstalling the low-pressure EGR valve 65 or installing a new low-pressure EGR valve 65 can be facilitated.

As described above, the dimension L3 of the gap G is selected such that the first gasket 68 and the second gasket 69 in an unused state can be inserted between the low-pressure EGR valve 65 and the second low-pressure EGR pipe 64 and between the low-pressure EGR valve 65 and the joint member 71. More specifically, as shown in FIG. 6, with the low-pressure EGR valve 65 installed in the designated position, a gap t3 greater than the thickness of the first gasket 68 in the unused state is created between the low-pressure EGR valve 65 and the second low-pressure EGR pipe 64, and a gap t4 greater than the second gasket 69 in the unused state is created between the low-pressure EGR valve 65 and the joint member 71. Therefore, the first gasket 68 and the second gasket 69 can be installed in the designated positions after the low-pressure EGR valve 65 is installed without any difficulty. Thereafter, the remaining parts of the low-pressure EGR valve 65 and the associated parts can be assembled by reversing the order of disassembly discussed earlier.

According to the low-pressure EGR device 60 constructed as described above, the following advantages can be obtained. As shown in FIG. 4, the inlet end of the low-pressure EGR valve 65 is detachably connected to the second downstream flange 64 b of the second low-pressure EGR pipe 64, and the free end of the compressor connecting pipe portion 41 b is detachably connected to the outlet end of the low-pressure EGR valve 65. The flexible pipe member 72 connected to the compressor connecting pipe portion 41 b and the joint connecting pipe portion 71 b by the hose bands 73 has a length L1 smaller than the distance L2 between the annular shoulder surface 41 c and the annular shoulder surface 71 c. Therefore, a gap G is created between the flexible pipe member 72 and the annular shoulder surface 41 c. As a result, the flexible pipe member 72 and the joint member 71 can be axially moved toward the side of the compressor 41 until the flexible pipe member 72 abuts against the annular shoulder surface 41 c so that the low-pressure EGR valve 65 can be easily removed without removing the compressor 41.

As shown in FIGS. 1, 3 and 4, the compressor 41 is provided so as to protrude beyond the left end of the engine 4, and the second downstream flange 64 b of the second low-pressure EGR pipe 64, the low-pressure EGR valve 65, the joint connecting pipe portion 71 b, the flexible pipe member 72 and the compressor connecting pipe portion 41 b are arranged in the fore and aft direction along the left side of the engine 4. Therefore, the low-pressure EGR device 60 can be arranged in a compact manner adjacent to the engine 4.

As shown in FIGS. 2 and 3, the first upstream flange 62 a of the first low-pressure EGR pipe 62 is connected to a portion of the exhaust system 30 on the downstream side of the catalytic converter 33, and the compressor connecting pipe portion 41 b is connected to the upstream side of the compressor 41. Therefore, the exhaust gas contains moisture with a certain acidity, but the acidity of the exhaust gas is weakened as the exhaust gas passes through the catalytic converter 33 before the exhaust gas is recirculated to the intake air of the intake system 20 under negative pressure via the low-pressure EGR device 60. Therefore, deterioration of the flexible pipe member 72 that could be caused by the acidity can be minimized.

As shown in FIG. 3, the low-pressure EGR device 60 includes the low-pressure EGR cooler 63 fixedly attached to the engine 4 and disposed between the engine 4 and the catalytic converter 33. In terms of the flow of the exhaust gas, the low-pressure EGR cooler 63 is provided with an intermediate part of the path of the exhaust gas or between the first low-pressure EGR pipe 62 and the second low-pressure EGR pipe 64. The low-pressure EGR device 60 extends from the first upstream flange 62 a to the left side of the engine 4 through a space defined between the engine 4 and the catalytic converter 33. The low-pressure EGR device 60 then extends toward the intake side of the engine 4 along the left side of the engine, and curves upward to be bent back toward the exhaust side of the engine 4. Therefore, the temperature of the exhaust gas flowing through the flexible pipe member 72 is lowered as the exhaust gas flows along this path so that the thermal degradation of the flexible pipe member 72 is minimized. Furthermore, the low-pressure EGR device 60 can be arranged in a highly compact manner by making use of the space defined between the engine 4 and the catalytic converter 33.

The second low-pressure EGR pipe 64 connecting the low-pressure EGR cooler 63 to the low-pressure EGR valve 65 is made of a rigid member and fixed to the engine 4. Therefore, the support rigidity of the second low-pressure EGR pipe 64 is very high. This facilitates the work of installing and removing the low-pressure EGR valve 65, and also eliminates the need to remove or install the low-pressure EGR cooler 63 when removing the low-pressure EGR valve 65 so that the need for the work involved in removing and filling cooling water for the low-pressure EGR cooler 63 can be eliminated.

As shown in FIGS. 4 and 5, as a fastening means for detachably fastening the second low-pressure EGR pipe 64, the low-pressure EGR valve 65, and the joint member 71 having the joint connecting pipe portion 71 b, at least one stud bolt 81 (more preferably at least two stud bolts) each penetrating the EGR valve 65 having a base end threaded into the joint member 71 is used. The free end of the stud bolt 81 is provided with a threaded position and the nut 83 is threaded thereon. Therefore, the low-pressure EGR valve 65 and the joint member 71 can be temporarily assembled to the second low-pressure EGR pipe 64 making use of the stud bolt 81 so that the assembling of the the low-pressure EGR device 60 is facilitated. In the illustrated embodiment, two stud bolts 81 are used as fastening means. Therefore, the relative position of the low-pressure EGR valve 65 in the direction perpendicular to the joint member 71 with respect to the joint member 71 is correctly determined while the EGR valve 65 and the joint member 71 are being temporarily assembled so that the assembling the low-pressure EGR device 60 is facilitated even further.

In the illustrated embodiment, the base end of each stud bolt 81 is screwed into the joint flange portion 71 a of the joint member 71, but may also be threaded into or otherwise detachably fastened to the second downstream flange 64 b of the second low-pressure EGR pipe 64.

As shown in FIG. 4, each stud bolt 81 has a tool engaging feature 81 a at the free end. Further, the stud bolt 81 protrudes from the second downstream flange 64 b by more than twice the thickness of the nut 83 in the assembled state so that an additional nut 84 may be threaded onto the free end of the stud bolt 81. Therefore, even when the stud bolt 81 is firmly lodged in the threaded hole 70 of the joint flange portion 71 a, the stud bolt 81 can be unscrewed from the threaded hole 70 by applying an unfastening torque to the additional nut 84 with a suitable tool. Since the additional nut 84 has a relatively large diameter, a large unfastening torque can be applied to the stud bolt 81.

As shown in FIGS. 4 and 6, the dimension L3 of the gap Gin the axial direction of the flexible pipe member 72 is selected such that the first gasket 68 and the second gasket 69 in an unused state can be fitted into the gap between the low-pressure EGR valve 65 and the second low-pressure EGR pipe 64 and the gap between the low-pressure EGR valve 65 and the joint member 71, respectively. More specifically, when the flexible pipe member 72 is moved leftward until the corresponding end of the flexible pipe member 72 abuts the annular shoulder surface 41 c, the gap (t3) created between the low-pressure EGR valve 65 and the second low-pressure EGR pipe 64 and the gap (t4) created between the low-pressure EGR valve 65 and the joint member 71 are larger than the thicknesses of the first gasket 68 and the second gasket 69 in an unused state. Therefore, the removal and reinstalling of the low-pressure EGR valve 65 can be accomplished with ease.

Although the present invention has been described in terms of a preferred embodiment thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the spirit of the present invention. For instance, the present invention was applied to an automotive diesel engine, but may also be applied to gasoline engines as well, and may also be applied to engines for other applications, such as railways and other ground transportation vehicles, watercraft and aircraft.

Further, in the above-described embodiment, the engine 4 was laterally mounted on the motor vehicle 1, but may be mounted longitudinally. The exhaust side of the engine may also be provided on the opposite side of the engine without departing from the spirit of the present invention. In the foregoing embodiment, the EGR device was applied to the low-pressure EGR device 60, but may be applied to the high-pressure EGR device 50. In the above embodiment, the turbocharger 40 may be replaced with a supercharger which may be powered either by an electric motor or the output of the engine. In the above embodiment, the compressor connecting pipe portion 41 b was formed integrally with the compressor housing 41 a, but may also be formed separately from the compressor housing 41 a and coupled to the compressor housing 41 a. In the above embodiment, two stud bolts 81 were implanted in the joint member 71, but one or three or more stud bolts 81 may be used, and the stud bolts 81 may also be implanted to the second low-pressure EGR piping 64. Alternatively, it is also possible to do away with the stud bolts 81 altogether, and use only normal threaded bolts.

In the above embodiment, the stud bolts 81 and the normal bolt 82 were passed through the valve housing 65 a of the low-pressure EGR valve 65, and the second low-pressure EGR pipe 64, the low-pressure EGR valve 65 and the joint member 71 were fastened together by the nut 83. However, a fastening means for fastening the second low-pressure EGR pipe 64 and the low-pressure EGR valve 65 to each other and a fastening means for fastening the low-pressure EGR valve 65 and the joint member 71 to each other may be separately provided.

Alternatively, fasteners other than bolts and nuts may be used for the fastening member. In the above embodiment, the gap G was formed between the annular shoulder surface 41 c and the flexible pipe member 72, but it may also be formed between the annular shoulder surface 71 c and the corresponding end of the flexible pipe member 72. Furthermore, the compressor connecting pipe portion 41 b and the joint connecting pipe portion 71 b may not be exactly aligned in a coaxial relationship, and/or the flexible pipe member 72 may be bent or otherwise curved. 

1. An EGR device for a multiple-cylinder engine equipped with a supercharger for returning a part of exhaust gas expelled from an exhaust system of the engine to an intake system of the engine, comprising: a first connecting pipe portion extending from a compressor of the supercharger and having a first annular shoulder surface at a base end thereof; an EGR valve fixedly attached to a part of the engine; a joint member including a flange attached to the EGR valve and a second connecting pipe portion defining a passage communicating with an inlet end of the EGR valve, and opposing the first connecting pipe portion in a coaxial relationship, the second connecting pipe portion being provided with a second annular shoulder surface at a base end thereof; and a flexible pipe member having a first end fitted onto the first connecting pipe portion and a second end fitted onto the second connecting pipe portion; wherein a distance between the two annular shoulder surfaces is greater than a length of the flexible pipe member by a prescribed distance.
 2. The EGR device according to claim 1, wherein the supercharger consists of a turbocharger including a turbine for powering the compressor and attached to a part of the engine such that the compressor projects from an exhaust side part of the engine beyond a cylinder row end part of the engine, and the first connecting pipe portion, the EGR valve, the flexible pipe member and the second connecting pipe portion extend from the compressor along the cylinder row end part of the engine.
 3. The EGR device according to claim 2, further comprising an upstream EGR pipe assembly communicating a part of the exhaust system to the inlet end of the EGR valve, the upstream EGR pipe assembly including a part extending generally vertically along the cylinder row end part of the engine toward a downstream part of the exhaust system of the engine.
 4. The EGR device according to claim 3, wherein an exhaust gas purification device is positioned on an exhaust side of the engine under the turbine, and an upstream end of the upstream EGR pipe assembly is connected to a downstream part of the exhaust gas purification device.
 5. The EGR device according to claim 4, wherein the upstream EGR pipe assembly extends generally upward from the upstream end thereof between the engine and the exhaust gas purification device, and along the cylinder row end part of the engine toward the intake side of the engine before doubling back toward the exhaust side of the engine and being connected to the inlet end of the EGR valve.
 6. The EGR device according to claim 5, wherein the upstream EGR pipe assembly comprises an EGR cooler.
 7. The EGR device according to claim 6, wherein the upstream EGR pipe assembly includes a rigid pipe member connected between the EGR cooler and the EGR valve.
 8. The EGR device according to claim 7, wherein a plurality of threaded bolts are passed through a flange provided on a downstream end of the rigid pipe member of the upstream EGR pipe assembly, the EGR valve and the joint member to fasten these components to one another.
 9. The EGR device according to claim 8, wherein the threaded bolts include at least a pair of stud bolts each having a base end threaded into one of the flange of the rigid pipe member and the flange of the joint member, and a free end having a threaded portion having a nut fastened thereon.
 10. The EGR device according to claim 9, wherein the free end of each stud bolt is provided with a tool engagement feature.
 11. The EGR device according to claim 9, wherein the threaded portion on the free end of each stud bolt is provided with a length at least twice as long as a thickness of the nut.
 12. The EGR device according to claim 9, wherein a first gasket is interposed between the flange of the rigid pipe member of the upstream EGR pipe assembly and the EGR valve, and a second gasket is interposed between the EGR valve and the joint member, and wherein the distance between the two annular shoulder surfaces is greater than the length of the flexible pipe member at least by a combined thickness of the two gaskets in an unused state.
 13. The EGR device according to claim 9, wherein each end of the flexible pipe member is secured onto the corresponding connecting pipe portion with a hose band. 